The present invention relates to a method of coating a metal surface, such as the metal surface of a tool or an agricultural implement, with a hard, wear-resistant coating.
Coating a metal surface with another metal or metal alloy to enhance appearance, protect against corrosion, or improve resistance to wear is well known in the art of metallurgy. Coating tools, particularly cutting edges of tools, with a hard, wear-resistant alloy is a common industrial practice, especially in the art of agricultural implement fabrication, and is often referred to as "Hardfacing" or "hard surfacing." For example, see Alessi, U.S. Pat. No. Re. 27,852, Revankar U.S. Pat. No. 5,027,878 and No. 5,443,916, Brady, et al., U.S. Pat. No. 4,682,987, and Hill U.S. Pat. No. 5,456,323.
Hardfacing is often done by fusing a powdered, hard metal alloy onto a metal surface. Typically, this method involves coating the metal surface with an aqueous slurry of a powdered, homogeneous alloy, a powdered flux, a binding agent, and a suspension agent; drying the slurry to form a solid layer; and heating the metal surface to a sufficiently high temperature to fuse the alloy onto the surface. The flux is to protect the alloy from reacting with the gases in the fusing furnace atmosphere while the alloy is being heated. The suspension agent promotes a uniform slurry. The binder holds the alloy and flux powders in place until the alloy slurry has dried onto the metal surface.
One problem with this method of hardfacing is that the flux, binder and suspension agent additives in the slurry remain in the fused coating as undesirable nonmetallic inclusions, and reduce the volume of effective wear-resistant coating for a given coating thickness. These inclusions are discontinuities in the coating that increase its brittleness and thus promote coating material removal by fracture, rather than abrasive wear, resulting in premature wear and shorter wear life of the coating.
Another problem with the methods of the art is nonuniformity of coating thickness. There are two reasons of this problem. 1) The slurry application allows the slurry to flow, when wet, on vertical and sloping surfaces thus forming an uneven distribution of the powdered alloy. 2) The flux/binder mixture used in the coating slurry melts ahead of the coating powder, and the resulting liquid tends to displace the powder particles on vertical and sloping surfaces and nonuniformly distribute them before the alloy powder begins to fuse.
It is an object of the present invention to provide a method for uniformly hardfacing a metal surface with a wear-resistant alloy with substantially no nonmetallic inclusions. A second object is to provide a slurry of wear-resistant alloy for use in hardfacing.